My 1991 7.3 idi is making a rod knock sounding noise when cold but goes away once at full temp. I am running 100% wmo in the truck filtered to 10 micron through a huge filter. I can only hear the noise under the truck and near the drivers door. The noise is most noticeable at the drivers rear of the cab. The truck has a smf conversion, with a zf5 manual conversion. The truck has lots of power for an N/A, and reads in the middle for oil pressure on the stock guage at all times. I have also just rebuilt the heads with all new guides, and seals. Could this be an injector? When warm it doesnt smoke but when cold it smokes blue good since its on wmo. What would piston slap or rod knock be like? Thanks.
Engine knock
- Thread starter BigDiesel
- Start date
Could very well be an injector or it could be that the pump is advanced too far and the cold advance makes it worse. Try unplugging the cold advance when you first start it and see if it doesn't go away. It is probably just an injector failing and firing earlier and this is made worse by the cold advance.
The timing is good since I timed it by ear to rattle a bit when cold and be quiet when hot. The truck overall runs alot quieter on WMO then on diesel. When at full temp running it around 1300-1700 at part load I can hear a faint ball pein hammer noise which is more noticeable on WMO then on diesel. The truck has 186,000 miles on it and still has 6 original injectors. I changed 2 to find a bad valve guide. I will try the advance solenoid unplug tommorow. Thanks.
k_williams1982
'01 Excursion 4x4
It's on the top of the IP. I believe the wire clip closest to the grille is the fuel cutoff solenoid, and the one towards the firewall is the advance solenoid. Someone will correct me if I'm wrong.
You are right, or at least that is how mine is.
I find it beneficial and necessary to occasionally run about 3 tanks of streight diesel through the Moosestang (which has a heavy WMO diet) in order to "clean it out". Your knock may be due to injector cokeing. If you haven't pulled them in a while, you might want to take a look and see what the hole the injector sits in looks like. Last time I pulled mine, about half were coaked up pretty bad, and I needed to use an ice pick to break it up.
With unplugging the solenoid the knock is still present. On WMO the engine is quiet when cold, and even quieter when at full temp. I ran diesel on the way home from work (30kms) and it seemed to get rid of the knock but the knock on WMO goes completely away once at full temp. I will see if its present tomorrow when I start it up cold. The knock i noticed can be heard at the top of the engine and at the bottom. Thanks.
